Apparatus for making high intensity discharge arc tube

ABSTRACT

A quartz tube is held in a lathe and rotated while heat is applied to an intermediate portion thereof. When the quartz is heated to plasticity, rotation is stopped and a mold is rapidly closed around the softened quartz. The quartz is shaped in the mold by the rapid application of gas pressure in the tube.

United States Patent m Finch et al.

[4 1 Sept. 16, 1975 l l APPARATUS FOR MAKING HIGH INTENSITY DISCHARGE ARC TUBE [75] Inventors: William A. Finch. Marhlehead;

Frederick A. Loughridge, Ipswich; Rudolf Marcucci, Beverly, all of Mass.

[73] Assignee: GTE Sylvania Incorporated,

Danvers, Mass.

[22] Filed: Aug. 22, 1973 [2|] Appl. No.: 390,538

[52] U.S. Cl. 4. 65/279; 65/l09; 65/292 (5 l] Int. Cl. C03B 23/14 [58] Field of Search 65/109, H0. 276, 279 65/292 [56} References Cited UNITED STATES PATENTS 3 3U9.l88 3/l967 Porter et al (IS/IQ) OTHER PUBLICATIONS Alien Property Custodian published application Se rial No. 4l8 6()3, Dichter.

Primary ExuminerArthur D. Kellogg Armrney, Agent, or Firm-James Theodosopoulos 5 7 1 ABSTRACT A quartz tube is held in a lathe and rotated while heat is applied to an intermediate portion thereof. When the quartz is heated to plasticity, rotation is stopped and a mold is rapidly closed around the softened quartz. The quartz is shaped in the mold by the rapid application of gas pressure in the tube.

l Claim, 1 Drawing Figure 3 .VUSTQS APPARATUS FOR MAKING HIGH INTENSITY DISCHARGE ARC TUBE BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates to are tubes for high intensity discharge (HID) lamps and especially to apparatus and method of making such are tubes.

2. Description Of The Prior Art The arc tubes of high intensity discharge lamps have generally consisted of cylindrical uniform diameter tubes of vitreous quartz or other high temperature glass. Such tubes were prepared by merely cutting long lengths of extruded tubing to the desired length. Electrodes were then sealed in the ends of the arc tube and the arc tube was then exhausted and filled through an exhaust tube attached thereto. which was then tipped off to complete fabrication of the arc tube.

SUMMARY OF THE INVENTK )N This invention concerns the manufacture of an arc tube which does not consist ofa cylindrical uniform diarnctcr tube as in the prior art. Such an arc tube may have an arch shape. as disclosed in copcnding application Ser No. 377,441. filed July 9. I973. entitled Metal Halide Discharge Lamp Having An Arched Arc Tube", now US. Pat No. F,l 58.()78 or an expanded section. as disclosed in copcnding application 380.737. lilcd July 19. I973 entitled Metal Halide Discharge lamp Having Expanded Section Arc Tube." the disclosures of which are incorporated herein by reference.

In the manufacture ofan arc tube in accordance with this invention, a straight length of cylindrical quartz tubing is rotatablyI held. such as in the chucks ofa lathe.

One end of the tubing is closed and the other end is connected to a supply of pressurized gas. While the tubing is rotated. an intermediate portion thereof is heated by a high temperature flame using. for etample, a ribbon burner. When the plastic or working temperature of the quartz. is attained. about 1.8UU to l.9(lll(. the rotation is stopped. the burner is moved out of the way and two mold halves are rapidly closed around the heated quartz. As soon as the lnold is closed. gas pressure is introduced into the tubing to blow the heated quartz into the shape oftbe mold. Because the working temperature ofthe quartz is so high. it is necessary that the shaping of the tubing be extremely rapid. say. less than about one second after the flame is removed. lest the heated quartz cool below its working temperature. After the shaped tubing is removed from the mold. the excess tubing length is severed and the arc tube is ready for completion.

BRIEF DhSCRlPTION OF THE DRAWING l'he single ll(iLlRl-' in the drawing is a perspective \icw olapparatus for the manufacture oi'HII) arc tubes in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The ends of a length of quart? tubing, longer than the finished arc tube and having a thicker wall than that of the finished arc tube. are supported in two collet type chucks I (only one is shown in the drawing). One end of the tubing is closed. such as by a stopper or by use of a blind hole type of collet. and the other end is attached, through the chuck. to a supply of pressurized gas (not shown). In one example, the tubing was 9 inches long by 12 mm diameter.

Upon actuation of a sequence starter button, the chucks start rotating and slide 2 is moved backward against a stop 3 to bring ribbon burner 4 into position proximate the quartz tubing. burner 4 being supported on slide 2. At the same time a microswitch 5 is energized by slide 2, which ignites burner 4 by means of a solenoid. Heat is applied to the rotating quartz tubing until it is heated to plasticity, that is, its working tern perature. about lflUtV-ISUUT. When the temperature is reached. slide 2 is energized and moved forward by air cylinder 6 against stop 7. which mox es burner 4 out of the way. At the same time. top and bottom molds 8 and 9, which are supported on slide 2. are moved into position above and below the heated quartz tubing. burner 4 is turned off and the chucks stop rotating. lhe movement of slide 2 also energizes microswitchcs l0 and I1. l\/Iicroswitch I0 activates air cylinder 12 which closes molds 8 and 9 onto the heated quartz tubing. Microswitch ll energizes a solenoid (not shown) which o en a valve and admits ressurized gas into one end of the quartz tubing. In one example, the gas was nitrogen at a pressure of [2 psi. The pressurized gas blows the softened quartz into the shape of molds 8 and 9. The whole sequence. from burner removal to shaping of the tubing. takes less than about one second.

After cooling and rcmoval from the mold. an intermediate portion ot the tubing has been molded into the desired arc tube shape. whilc tubing portions at each end thereof are in a form suitable for the subsequent sealing of electrodes into the arc tube. The end por tions of the tubing. which include the portions held in the chucks. are severed prior to cmbedment of the electrodes in the are tube. In the specific example men" tioned above, the molded are tube was about 2 inches long and had an arch shape. with an outside diameter of If mm. The seal portions at each end thereof had a length of about 1 inch and a diameter of about 13 mm. The end portions of the tubing, about 2% inches each. were severed. The are tube was completed by attaching an exhaust tube thereto. scaling electrodes in press seals at the ends of the arc tube. exhausting and filling the arc tube with. for example. an inert starting gas. mercury and metal halide through the exhaust tube and then tipping oil the exhaust tube.

In order to improve the material efficiency. that is. to reduce the amount of quartz that is discarded at the ends ofeach arc tube after molding. it may be desirable to start with an original length of quartz tubing that is sufficiently long so that a plurality of arc tubes may be formed from it. The are tubes may then be individually shaped by a single mold pair, or may be shaped at one time by a number of molds in alignment with each other. In this case only the portions of the tubing held in the chucks need be discarded after molding.

We claim:

I. Apparatus for the manufacture of arc tubes for high intensity discharge lamps comprising: means for holding and rotating a length of vitreous quartz tubing: a heater for heating an intermediate portion of the quartz tubing to a temperature of at least about 1.800%. said heater being mounted on a slidable support. said heater in its heating position being proximat said intermediate portion of quartz tubing: a closablc two piece mold mounted on said slidable support; means for rapidly moving said slidable support. upon intermediate portion of quartz tubing; and means for introducing pressurized gas into the interior of the quartz tubing and forming said intermediate portion into the mold shape in less than one second after removal] of the heater. 

1. APPARATUS FOR THE MANUFACTURE OF ARC TUBES FOR HIGH INTENSITY DISCHARGE LAMPS COMPRISING: MEANS FOR HOLDING AND ROTATING A LENGTH OF VITREOUS QUARTZ TUBING: A HEATER FOR HEATING AN INTERMEDIATE PORTION OF THE QUARTZ TUBING TO A TEMPERATURE OF AT LEAST ABOUT 1,800*C, SAID HEATER BEING MOUNTED ON A SLIDABLE SUPPORT, SAID HEATER IN ITS HEATING POSITION BEINB PROXIMATE SAID INTERMEDIATE PORTION OF QUARTZ TUBING: A CLOSABLE TWO PEICES MOLD MOUNTED ON SAID SLIDABLE SUPPORT: MEANS FOR RAPIDLY MOVING SAID SLIDABLE SUPPORT, UPON ATTAINMENT BY SAID INTERMEDIATE PORTION OF QUARTZ TUBING OF SAID TEMPERATURE, SO AS TO MOVE SAID HEATER AWAY FROM ITS POSITION PROXIMATE SAID INTERMEDIATE PORTION OF QUARTZ TUBING AND TO MOVE SAID TWO PIECE MOLD INTO POSITION PROXIMATE SAID INTERMEDIATE PORTION 